1. Field of the Invention
The present invention relates to a dielectric ceramic composition used as a dielectric layer of an electronic device, such as a multilayer ceramic capacitor, a production method thereof, and an electronic device comprising the dielectric ceramic composition as the dielectric layer.
2. Description of the Related Art
A multilayer ceramic capacitor as an example of electronic devices is produced, for example, by printing internal electrodes in a predetermined pattern on a ceramic green sheet formed by a predetermined dielectric ceramic composition, alternately stacking the results to make it as one body, and co-firing a thus obtained green chip. Since internal electrode layers of the multilayer ceramic capacitor are formed to be one body with ceramic dielectric by firing, materials not reacting with the ceramic dielectric has to be selected. Therefore, in the related art, it has been necessary to use expensive precious metals, such as platinum and palladium, as the material composing the internal electrode layer.
In recent years, however, dielectric ceramic compositions using inexpensive base metals, such as nickel and copper, have been developed and a drastic reduction of costs has been realized.
Also, in recent years, demands for downsizing of electronic devices have become stronger along with electronic circuits becoming higher in density, and multilayer ceramic capacitors have rapidly become downsized with a larger capacity. To attain a downsized multilayer ceramic capacitor with a larger capacity, a method of making dielectric layers thinner and a method of heightening specific permittivity of a dielectric ceramic composition included in dielectric layers, etc. have been generally used. However, when dielectric layers are made thin, an electric field imposed on the dielectric layers becomes stronger at the time of applying a direct current voltage, consequently, there has been a disadvantage that a change of the specific permittivity with time, that is, a change of the capacity with time becomes remarkably large.
To improve a change of the capacity with time under a direct current voltage, there has been proposed a method of using dielectric particles having a small average crystal grain diameter as dielectric particles to be included in the dielectric layers (for example, refer to the Japanese Unexamined Patent Publication No. H08-124785). The Japanese Unexamined Patent Publication No. H08-124785 discloses a dielectric ceramic composition having a specific composition, wherein an average crystal grain diameter of the dielectric particles is 0.45 μm or smaller. However, the dielectric ceramic composition described in the article has too low specific permittivity to respond to downsizing and obtaining of a larger capacity.